System for operating multiple position display tubes

ABSTRACT

The disclosed system is adapted for operating multiple position display devices having a plurality of groups of display cathode segments or elements positioned side-by-side, with corresponding elements being electrically interconnected and each group having an associated anode, and an auxiliary electrode common to all of the groups of electrodes for preventing spurious glow about them. The drivers for the anodes are coupled in parallel through suitable impedances to a common impedance from which is taken proportional potential for biasing the auxiliary electrode responsive to the pulsed operation of the anodes. The cathode drivers are also optionally coupled to the common impedance or the auxiliary electrode itself for negatively influencing the auxiliary electrode potential as a function of the number of cathode segments being energized, to aid in preventing spurious glow during operation of the device at high current levels.

United States Patent 1191 Glaser Jan. 7, 1975 SYSTEM FOR OPERATINGMULTIPLE [57] ABSTRACT POSITION DISPLAY TUBES 7 51 Inventor; DavidGlaser Greenbmbk Ni The disclosed system is adapted for operatingmultiple position display devices having a plurality of groups of [73]Asslgnee: P' corpmatmnt Detroltt display cathode segments or elementspositioned sideby-side, with corresponding elements being electri- [22]Filed: Feb. 20, 1973 cally interconnected and each group having anassociated anode, and an auxiliary electrode common to all [21] Appl-333,496 of the groups of electrodes for preventing spurious RehtedApplication Data glow about them. The drivers for the anodes are cou-[63] Continuation of Ser. 139 543 May 3 1971 pled in parallel throughsuitable impedances to a comabandone mon impedance from which is takenproportional po tential for biasing the auxiliary electrode responsiveto [52] Cl 315/169 TV, 315/169 R, 340/336, the pulsed operation of theanodes. The cathode driv- 3l3/517 ers are also optionally coupled to thecommon imped- 51 Int. Cl. H05b 37/00 or the auxiliary Ode itselfnegaive'y 581 Field of Search 313/109, 5, 210; fluencing the auxiliaryelectrode Potential as a func- 315/169 TV, 169 340/336 tion of thenumber of cathode segments being energized, to aid in preventingspurious glow during opera- [56] References Cited tion of the device athigh current levels.

UNITED STATES PATENTS 3,509,420 4/1970 Ogle 315/169 R X PrimaryExaminer-I-Ierman Karl Saalbach Assistant ExaminerLawrence J. DahlAttorney, Agent, or FirmGeorge L. Kensinger; Kenneth L. Miller; RobertA. Green Claims, 3 Drawing Figures SEQUENCER 1210 13 253 Is 293 251 258k 291 298 A V W230 t 2| 14o s A r\ l 0 2| 4| 51 9| i 3,859,559 SHEET 10F2 PAT-ENTED 7 I975 ATTORNEY PATENTEDJAN 1% sum 2 or 2 mmUZm30mmINVENTOR.

DAVID GLASER ATTORNEY SYSTEM FOR OPERATING MULTIPLE POSITION DISPLAYTUBES This is a continuation, of application Ser. No. 139,543, filed May3, 1971, now abandoned.

BACKGROUND OF THE INVENTION The subject invention relates to a systemfor operating multiple position display panels having a plurality ofinterconnected cathode elements for displaying characters in one or morerows. More particularly, the invention relates to the operation ofmultiple position gas discharge devices having segmented cathodeelectrodes and a plurality of individual anode electrodes for displayingcharacters side-by-side.

A multiple position display device which is available commercially isknown as the PANAPLEX numeric panel display. Such display panels includea plurality of groups of cathode elements in the form of elongated barsor segments. Each group of segments is configured in a figure 8 patternor the like and the various segments can be energized in differentgroups, together with an anode, to represent different characters asselected positions in the device. Electrical discharge in the device atthe selected group of electrodes ionizes the gas and results in cathodeglow about the cathode elements which displays the desired character.

Some such display devices include an auxiliary electrode which is commonto all the groups of electrodes and is to be biased at a potentialintermediate the cathode and the anode potentials to prevent spuriousglow in the, device as described in Harvey, et al., Ser. No. 78,045,filed Oct. 5, 1970, now abandoned. Under some circumstances, however,spurious glow sometimes develops in an adjacent group of electrodes orbetween adjacent electrode groups when a particular anode is energized.Only one group of cathode segments should glow at such time.

These problems were solved satisfactorily for many conditions ofoperation in Holz and Dieterman Ser. No. 85,662, filed on Oct. 30, 1970,in G. E. Holz Ser. No. 87,058, filed Nov. 5, 1970, and in E. L. HarveySer. No. 126,825 and Doane, et al., Ser. No. 126,825, filed on Mar. 22,1971.

However, under some circumstances, and particularly when the cathodesare driven at high levels of current for a brighter display, spuriousglow still occurs. Also, separate circuitry was provided in theseapplications for biasing and limiting the potential on the cathode andauxiliary electrodes separate from the anodes. This tends to be costlyto implement.

SUMMARY OF THE INVENTION Accordingly, an object of this invention is toimprove spurious glow suppression in mulitple position display deviceshaving interconnected cathode elements or segments.

Another object of the invention is to further simplify and reduce thecost of systems for operating multiple position display devices havingauxiliary electrodes for spurious glow suppression.

In accordance with the invention, a system for operating multipleposition display devices includes a driver for each anode coupled inparallel through suitable impedances to a common impedance from which istaken a proportional biasing potential for application to the auxiliaryglow suppression electrode. The potential applied to the auxiliaryelectrode follows the pulsed operation of the anodes for preventingspurious glow among the display electrodes. No steady-state or DCbiasing potential, accordingly, need be applied to the auxiliaryelectrode either initially or during operation of the display controlelectrodes.

Additionally, each of the electrode drivers is also optionally coupledto the common impedance means for reducing the auxiliary electrodepotential as a function of the number of cathode segments beingenergized. This improves the suppression of spurious glow in the deviceand permits the use of higher current levels without spurious glow aboutthe electrodes than otherwise possible, which provides a brighterdisplay of the desired characters or symbols.

DESCRIPTION OF THE DRAWINGS These and other advantages and features ofthe invention are made clear in the following detailed descriptionrelating to the attached drawings wherein:

FIG. 1 is a perspective view of a portion of 21 segmented cathodedisplay tube having individual anodes and an auxiliary electrode adaptedto be operated by the system of the invention;

FIG. 2 is an elevational view of a longitudinal section of the displaypanel or tube of FIG. 1; and

FIG. 3 is an electrical schematic diagram of the system of theinvention, including a schematic representation of the display devicebeing operated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the inventionare particularly applicable to operation of the type of display devicedescribed and claimed in the Harvey, et al., patent application Ser. No.217,781, filed Jan. 14, 1972. Some of the features of such a device areshown in FIGS. 1 and 2 ofa display panel or tube 10 having threerepresentative display positions. A plurality of groups of cathodesegments 41-47, 5157, 61-67, are connected to corresponding conductors21-27 which are insulated from each other on an insulating base plate 20or within grooves in its surface as shown in FIG. 2. An anode electrode140, 150, 160, is provided or each group of cathode segments. Aninsulating sheet or layer 30 shields cathode conductors 21-27 from theanodes, as shown in FIG. 2, to prevent them from glowing.

The anodes in FIG. 1 are each shown as a ring surrounding the associatedgroup of cathodes, but they may be screen electrodes situated above theassociated cathode groups, or they may take any other desired shape. Inaddition, the device includes an auxiliary electrode 230 in the form ofa screen disposed above the groups of cathodes and anodes andelectrically associated with all of the electrode groups. Top and bottominsulating plates 200 and 20, respectively, sealed together by glass orceramic frit 15 or the like, complete the panel or tube structure.

Briefly, in operation of the display device shown in FIGS. 1 and 2,drive signals are applied to the cathode via conductor 21-27 inaccordance with the input information. Simultaneously, the anodes areenergized in turn from left to right, or in any other desired order orsequence via leads 34, 35, 36, in synchronism with the cathode drivesignals to cause the cathode segments in the selected groups to glow. Asuitable bias potential intermediate the cathode and anode biaspotentials is applied to lead 235 of screen electrode 230 for preventingspurious glow about the cathode segments and between adjacent displaypositions; The biased auxiliary electrode prevents extraneous dischargesfrom occurring between an energized anode and the cathodes in adjacentgroups which have operating potential applied to them.

A preferred embodiment of the invention is illustrated in FIG. 3 inwhich display device l'is shown schematically. Display segments 41, 51,91 are connected to cathode conductor 21 which is driven from thecollector of transistor 121. Likewise, cathode segments 42-92 through47-97 are connected to the collectors of cathode drivers 122-127 byconductors 22-27, respectively. Cathode conductors 21-27 are alsocoupled to one end of common resistor 19 at circuit junction 16 byresistors 111-117, respectively. The other end of resistor 19 isgrounded, as shown.

The base electrode of cathode driver transistors 121 through 127 areconnected to the ouput terminals of data source 100, respectively, forreceiving positivegoing information signals. The emitter electrodes ofcathode drivers 121-127 are coupled to the anode of diode 130 bycurrent-limiting resistors 9 1-97, respective ly. The cathode of diode130 is connected to a reference potential terminal 135, as shown.

Anode lead 34 of anode 140 is connected to the collector electrode ofanode driver transistor 240. Similarly, anode leads 35-39 of anodes150-190 are connected to the collector electrodes of anode drivers250-290. Anode leads 34, 35, 39 are also coupled to the end ofresistor'19 at circuit junction 16 by resistors 248, 258, 298,respectively. The emitter electrodes of anode drivers 240, 250, 290 arebiased from E reference terminal 12 through forward-biased diodes 13,the anodes of which are connected to the E reference terminal as shown.

Anode drivers 240-290 are controlled by sequencing circuit or device210. The base electrodes of the anode drivers are coupled to the outputterminals of the sequencer 210 by the series connection of resistor 241and capacitor 244, resistor 251 and capacitor 254, resistor 291 andcapacitor 294, respectively. The base electrodes of the drivers 240-290are biased by resistors 245, 255, 295 and diodes 246, 256, 296,respectively, to E reference potential terminal, as shown.

Coupling capacitors 244, 254, 294 provide DC level-shifting of thecontrol signals applied to the anode drivers. They permit sequencingcircuit 210 to be operated at the same signal and bias .levels as datasource 100 and cathode drivers 121-127, despite the different DC biaslevels in the anode and cathode circuits, themselves. This is necessarywhen integrated circuits or common transistor circuits are utilized inthe signal sources.

Diodes 242, 252, 292 have their cathodes connected to the junction ofthe series input resistors, and capacitors 241 and 244, 251 and 254, 291and 294, for clamping the anode control signals in the negativedirection to the potential limit applied to their anodes from terminal225. Diodes 243, 253, 293 have their anodes coupled to the junction ofthe respective input coupling resistors and capacitors to clamp thepositivegoing anode control signals at ground, as shown.

Auxiliary electrode 230 is usually biased at a potential intermediatethe anode bias potential E and the cathode bias potential E The biaspotential for the auxiliary electrode is usually taken from a voltagesource having considerable internal impedance or from a voltage divideror the like coupled to the anode or cathode bias terminal. Duringoperation, auxiliary electrode 230 then conducts a leakage current fromwhichever anode electrode -190 that is energized, into the associatedvoltage source or divider. This raises the potential on the auxiliaryelectrode as more cathode segments are energized or as the cathodes areactivated more rapidly. In certain improved circuits the cathode driversare also coupled to the voltage divider or bias impedance for biasingthe auxiliary electrode as an inverse function of the number of cathodesegments that are being energized.

In the present invention, electrode 235 of auxiliary electrode 230 iscoupled to circuit junction 16 between the anode drivers and resistor 19by resistor 237. Any other suitable impedance device may be substitutedfor resistors 19 and 237, if desired.

The bias potential that is applied to auxiliary electrode 230 throughresistor 237 is determined by the current in resistor 19. The currentfor resistor 19, in turn, is conducted by whichever anode driver 240-290is energized. If the anode drivers are not activated, then the potentialat circuit junction 16 and on the auxiliary electrode may float at someintermediate level. This is not deleterious, however, since under thiscondition no information is being displayed by the device. Each timeananode driver is actuated to display a symbol, current is conducted toresistor 19 and the auxiliary electrode is biased. This bias on theauxiliary electrode follows the pulsed or sequential operation of theanodes and becomes nearly continuous when they are operated in rapidsuccession.

The amount of current conducted by common bias resistor 19 is determinedby its value and the values of resistor 237 and of resistors 111-117, ifthey are used, which shunt each other in parallel when cathode drivers121-127 are activated. The potential between E reference terminal 12 andground is divided across resistor 248, 258, 298, depending on whichanode driver is activated, and resistor 19. The major current path forthe common bias resistor is, therefore, through the conducting anodedriver. Another current path which raises the potential on auxiliaryelectrode 230 is from the selected anode driver through its anode to theauxiliary electrode, resistor 237, and resistor 19. The magnitude ofthis current is determined primarily by the values of the resistorssince the anode drivers are normally saturated when activated, thusoperating as voltage switches.

It is the potential across common bias resistor 19 which primarilybiases auxiliary electrode 230 as mentioned above. An auxiliary currentpath, however, is established from the conducting anode driver throughthe associated resistor 248, 258, 298, coupling resistor 237 andauxiliary electrode 230 to the energized cathodes and the correspondingactivated cathode drivers 121-127. Another auxiliary current path isfrom the conducting anode driver through the associated resistor 248,258, 298 and one or more of coupling resistors 111-117 to the activatedcathode driver(s) 121-127. These auxiliary current paths shunt or bypasscommon bias resistor 19 and, therefore, tend to drop the potential atcircuit junction 16 and on the auxiliary electrode230 as an inversefunction of the number of cathode segments which are energized.

The theory of operation of the inventioh is quite complex, but it isbelieved to be as follows. As panel is operated and each characterposition is energized, positive column glow tends to'and often formsbetween the newly energized anode and cathbdeswhich had been energizedat the prior character position and are now turned off. This isundesirable spurious glow. The auxiliary electrode 230, by assuming agenerally negative or cathode potential (proportional to the number ofcathodes which glow) as each character position is operated, shields"each arfode from prior cathodes and prevents positive column glow.

Either of these auxiliary current paths through coupling resistor 237or. through pull-down resistors 111-1 17 may be utilized satisfactorilyin some conditions. In high current operation of the device for abrighter displayiboth of them may be used. If both auxiliary currentpaths are relied upon, it should be noted that pull-down resistors111-117 may be alternatively connected directly to lead 235 of auxiliaryelectrode 230 rather than to the common bias resistor at circuitjunctipn 16, if desired.

Although the preferred embodiment of the invention h 0 been described indetail, it should be understood z rthat the present disclosure has beenby way of example i only. Many modifications and, variations of theinvention are possible in light of the above teachings. It is,

-therefore, to be understood that the invention may be practicedotherwise than as specifically disclosed.

What is.claimed is: v v i v l. A character display circuit fordisplaying any one of a plurality of characters in each of a pluralityof sideby-side character positions, comprising i v a plurality ofanodes, one in each of said character positions,

a plurality of groups of cathodes, each such group.

being associated with one of said anodes and being located in one ofsaid character positions','ea ch of cathodes selectively in response toa first set of input signals, v a plurality of anode selection circuitsfor selectively energizing said anodes, in synchronism with theselective energization of said cathodes, in response to 1 a second setof input signals, for displaying selected characters in each of saidcharacter positionsgby means of current flow from each anode throughsaid gas atmosphere and through the selected cathodes which make up saidselected characters,the' magnitude of current flow at each characterposibias circuit means for establishing a dynamic voltage bias on saidauxiliary electrode,

said bias circuit means including impedance means connected electricallyin series with all of said anode selection circuits for developing abias voltage each time any one of said anode selection circuits isenergized by an input signal and current flows therethrough, and circuitmeans electrically connecting said impedance means to said auxiliaryelectrode for supplying such bias voltage to said auxiliary electrode,and

circuit means connecting each said cathode driver across at least aportion of said impedance means, so as to modify the effective impedanceconnected to said auxiliary electrode as each such cathode driverenergizes one of said cathodes.

2. A character display circuit as in claim 1 wherein the plurality ofanodesand the plurality of groups of cathodes are all located within acommon gas-tight envelope,

and wherein the auxiliary electrode is a single electrode associatedwith each of the character positions and in operative relation to thecathodes and anodes in each such character position.

3. A character display circuit as in claim 2 wherein the auxiliaryelectrode contains a portion extending between the anode and cathodes ofeach character position and those of the next adjacent characterposition, to electrically isolate the electrodes of the respectivecharacter positions from each other.

4. A characer display circuit as in claim' 1 further including secondbias circuit means for dynamically biasing said cathodes withbiasyoltage pulses when said cathodes are not glowing, v i a,

i said second bias circuit means includinga plurality of biasingresistors, one for. each of said cathode conductors, each connectedbetween said impedance means and a different one of said cathode.conductors.. 5.- A character display circuit as in claim 4 wherein thecathode drivers are transistors, each connected to one of said cathodecondutors, andv I wherein each such transistor and-the biasing resistorwhich is connected to the same cathode conductor are connected inseries, and each of these resistortransistor series circuits isconnected acrossat least a portion of said impedance means. 6. Acharacter display circuit for displaying any one ofa plurality ofcharacters in each of a plurality of sideby -side character positions,comprising an envelope formed of a front plate with a viewing window anda rear plate, said plates being sealed I together along a predeterminedperimeter surrounding the side-by-side character positions to establisha gas tight, enclosure,

an ionizable gas within said enclosure at a pressure capable ofsustaining a cathode glow discharge,

a plurality of anodes one in each of said character positions withinsaid envelope, Y

a plurality of groups of cathodes, each such group being associated withone of saidanodes and being located in one of said characer positions,each of the cathodes having the shape of a segment of oneof thecharacters to be displayed,

a plurality of elongated conductors extending within said envelope, eachelectrically connected to one of the cathodes in each characterposition, and

each connected electrically to a terminal outside said envelope forconnection to an external circuit,

insulating material separating each of said conductors from all of thecathodes except the'cathode in each character position to which suchconductor is connected,

anode selection means for energizing said anodes sequentially andcathode selection means for simultaneously selectively energizingdifferent combinations of said cathode conductors sequentially, insynchronism with the sequential energization of the anodes, to form aside-by-side character display over all of said character positions,there being a current flow path from each anode through said ionizablegas in said envelope to its group of cathodes, with the magnitude ofcurrent flow at each character position as the anodes and cathodes areenergized being generally proportional to the number of cathodes whichare energized,

an auxiliary electrode associated with each of said character positionsand including a portion disposed between each anode and its group ofcathodes and an adjacent anode and its group of cathodes whereby eachanode is shielded from the adjacent group(s) of cathodes,

bias circuit means for establishing dynamic voltage bias on saidauxiliary electrode, said circuit means including at least one impedancedevice connected to said auxiliary electrode and connected electricallyin series with each such anode selection means for supplying to saidauxiliary electrode a series of bias voltage as said anodes aresequentially energized, one such voltage being generated during theenergization of each anode, each such bias voltage being inverselyproportional to the number of cathodes which glow at each characterposition, and

circuit means connecting said cathode drivers across at least a portionof said impedance device so as to modify the effective impedanceconnected to said auxiliary electrode as each cathode driver isenergized.

7. A character display circuit as in claim 6 wherein the bias circuitmeans serves to bias the auxiliary electrode to a predeterminedelectrical potential for isolating the anode and cathodes of eachcharacter position from those of all the other character positions, and

wherein as each cathode driver is energized, it reduces the effectiveimpedance connected to the auxiliary electrode.

8. A voltage compensated dynamic bias circuit for an auxiliary electrodein the gaseous atmosphere of a character indicator tube for displayingside-by-side characters, the tube having a plurality of anodes, one ineach character position, and a plurality of groups of cathodes eachlocated in one of the characters positions, the cathodes in each groupeach being in the shape of a segment of a character to be displayed,ineluding first circuit means including a pluralityof cathode conductorseach making electrical connection to one of the cathodes in eachcharacter position,

a plurality of cathode drivers, each connected to one of said cathodeconductors, for energizing different combinations of said cathodes inresponse to different combinations of electrical signals received bysaid cathode drivers,

anode selection circuit means for sequentially energizing said anodes,in sychronism with the selective energization of said cathodes, fordisplaying selected characters in each of said character positions,

bias circuit means for establishing a dynamic voltage bias on theauxiliary electrode, said circuit means including impedance meansconnected electrically to each of said anode selection circuits fordeveloping across said impedance means a series of bias voltage signalsas the anodes are sequentially energized, one such signal beinggenerated during the energization of each anode, and circuit meansclectrically connecting said impedance means to said auxiliary electrodeto supply such series of bias voltage signals to said auxiliaryelectrode, and

circuit means connecting said cathode driver across at least a portionof said impedance means so as to modify the effective impedanceconnected to said auxiliary electrode as each cathode driver isenergized.

9. Multiple-position display device and system for op erating thedevice, said device comprising a gas-gilled envelope including aplurality of groups of cathode electrodes and an anode electrodeassociated with each said group, each such group of cathode electrodesand its anode electrode comprising a character position in said displaydevice, corresponding cathodes of the different groups beinginterconnected by a single common conductor, there thus being a singlecommon cathode conductor for each cathode electrode in each of saidgroups, and an auxiliary electrode in operative relation with all ofsaid groups of cathode electrodes and their anode electrodes andincluding a portion disposed between each anode and the adjacent groupsof cathodes to act as a shield therebetween, said system comprising aseparate anode driver circuit connected to each said anode electrode insaid display device,

a sequencing circuit coupled to all of said anode drivers for turningeach one on separately and in turn whereby each anode can be connectedin circuit with a selected group of cathode electrodes,

a separate cathode driver circuit connected to each of said commoncathode conductors, each such driver circuit thus being connected to thesame corresponding cathode in each of said groups of cathodes,

a source of data signals coupled to said cathode driver circuits forenergizing a selected group of cathodes as each anode is connected incircuit, and

a common impedance connected in circuit with all of said anode driversand with all of said cathode drivers and with said auxiliary electrodewhereby at each said character position in said display deivice when acharacter is displayed by a selected number of cathode electrodes, abias voltage is developed across said impedance and is applied to saidauxiliary electrode, said bias voltage being related to the number ofcathode electrodes energized and exhibiting cathode glow and conductingcurrent at each character position.

10. Multiple-position display device and system for operating thedeivce, said device comprising a gasfilled envelope including aplurality of groups of cathode electrodes and an anode electrodeassociated with each said group, each such group of cathode electrodesand its anode electrode comprising a character position in said displaydevice, corresponding cathodes of the different groups beinginterconnected by a single common conductor, there thus being a singlecommon cathode conductor for each cathode electrode in each of saidgroups, and an auxiliary electrode in operative relation with all ofsaid groups of cathode electrodes and their anode electrodes andincluding a portion disposed between each anode and the adjacent groupsof cathodes and serving as a shield therebetween, said system comprisinga separate anode driver circuit connected to each said anode electrodein said display device,

a sequencing circuit coupled to all of said anode drivers for turningeach one on separately and in turn whereby each anode can be connectedin circuit with a selected group of cathode electrodes,

a separate cathode driver circuit connected to each of said commoncathode conductors, each such driver circuit thus being connected to thesame corresponding cathode in each of said groups of cathodes,

a source of data signals coupled to said cathode driver circuits forenergizing a selected group of cathodes as each cathode is connected incircuit;

a first current flow path from each of said anode drivers throughseparate resistive paths to all of said cathode drivers,

a second current flow path from each of said anode drivers through aresistive path to said auxiliary electrode, and

a third current flow path from each of said anode drivers to its anodeand through said display device to its group of cathode electrodes.

l l l

1. A character display circuit for displaying any one of a plurality ofcharacters in each of a plurality of side-by-side character positions,comprising a plurality of anodes, one in each of said characterpositions, a plurality of groups of cathodes, each such group beingassociated with one of said anodes and being located in one of saidcharacter positions, each of the cathodes having the shape of a segmentof one of the characters to be displayed, each of said anodes and itsassociated cathodes being disposed in an ionizable gas atmospherecapable of sustaining cathode glow discharge, a plurality of cathodeconductors each electrically connected to one of the cathodes in eachcharacter position, a plurality of cathode drivers, each connected toone of said cathode conductors, for energizing said cathodes selectivelyin response to a first set of input signals, a plurality of anodeselection circuits for selectively energizing said anodes, insynchronism with the selective energization of said cathodes, inresponse to a second set of input signals, for displaying selectedcharacters in each of said character positions, by means of current flowfrom each anode through said gas atmosphere and through the selectedcathodes which make up said selected characters, the magnitude ofcurrent flow at each character position being related to the number ofcathodes energized at such position, an auxiliary electrode in thegaseous atmosphere associated with each character position and includinga portion disposed between each anode and its group of cathodes and anadjacent anode and its group of cathodes whereby each anode is shieldedfrom the adjacent groups of cathodes, bias circuit means forestablishing a dynamic voltage bias on said auxiliary electrode, saidbias circuit means including impedance means connected electrically inseries with all of said anode selection circuits for developing a biasvoltage each time any one of said anode selection circuits is energizedby an input signal and current flows therethrough, and circuit meanselectrically connecting said impedance means to said auxiliary electrodefor supplying such bias voltage to said auxiliary electrode, and circuitmeans connecting each said cathode driver across at least a portion ofsaid impedance means, so as to modify the effective impedance connectedto said auxiliary electrode as each such cathode driver energizes one ofsaid cathodes.
 2. A character display circuit as in claim 1 wherein theplurality of anodes and the plurality of groups of cathodes are alllocated within a common gas-tight envelope, and wherein the auxiliaryelectrode is a single electrode associated with each of the characterpositions and in operative relation to the cathodes and anodes in eachsuch character position.
 3. A character display circuit as in claim 2wherein the auxiliary electrode contains a portion extending between theanode and cathodes of each character position and those of the nextadjacent character position, to electrically isolate the electrodes ofthe respective character positions from each other.
 4. A characerdisplay circuit as in claim 1 further including second bias circuitmeans for dynamically biasing said caThodes with bias voltage pulseswhen said cathodes are not glowing, said second bias circuit meansincluding a plurality of biasing resistors, one for each of said cathodeconductors, each connected between said impedance means and a differentone of said cathode conductors.
 5. A character display circuit as inclaim 4 wherein the cathode drivers are transistors, each connected toone of said cathode condutors, and wherein each such transistor and thebiasing resistor which is connected to the same cathode conductor areconnected in series, and each of these resistor-transistor seriescircuits is connected across at least a portion of said impedance means.6. A character display circuit for displaying any one of a plurality ofcharacters in each of a plurality of side-by-side character positions,comprising an envelope formed of a front plate with a viewing window anda rear plate, said plates being sealed together along a predeterminedperimeter surrounding the side-by-side character positions to establisha gas tight enclosure, an ionizable gas within said enclosure at apressure capable of sustaining a cathode glow discharge, a plurality ofanodes one in each of said character positions within said envelope, aplurality of groups of cathodes, each such group being associated withone of said anodes and being located in one of said characer positions,each of the cathodes having the shape of a segment of one of thecharacters to be displayed, a plurality of elongated conductorsextending within said envelope, each electrically connected to one ofthe cathodes in each character position, and each connected electricallyto a terminal outside said envelope for connection to an externalcircuit, insulating material separating each of said conductors from allof the cathodes except the cathode in each character position to whichsuch conductor is connected, anode selection means for energizing saidanodes sequentially and cathode selection means for simultaneouslyselectively energizing different combinations of said cathode conductorssequentially, in synchronism with the sequential energization of theanodes, to form a side-by-side character display over all of saidcharacter positions, there being a current flow path from each anodethrough said ionizable gas in said envelope to its group of cathodes,with the magnitude of current flow at each character position as theanodes and cathodes are energized being generally proportional to thenumber of cathodes which are energized, an auxiliary electrodeassociated with each of said character positions and including a portiondisposed between each anode and its group of cathodes and an adjacentanode and its group of cathodes whereby each anode is shielded from theadjacent group(s) of cathodes, bias circuit means for establishingdynamic voltage bias on said auxiliary electrode, said circuit meansincluding at least one impedance device connected to said auxiliaryelectrode and connected electrically in series with each such anodeselection means for supplying to said auxiliary electrode a series ofbias voltage as said anodes are sequentially energized, one such voltagebeing generated during the energization of each anode, each such biasvoltage being inversely proportional to the number of cathodes whichglow at each character position, and circuit means connecting saidcathode drivers across at least a portion of said impedance device so asto modify the effective impedance connected to said auxiliary electrodeas each cathode driver is energized.
 7. A character display circuit asin claim 6 wherein the bias circuit means serves to bias the auxiliaryelectrode to a predetermined electrical potential for isolating theanode and cathodes of each character position from those of all theother character positions, and wherein as each cathode driver isenergized, it reduces the effective impedance connected to the auxiliaryelectrode.
 8. A voLtage compensated dynamic bias circuit for anauxiliary electrode in the gaseous atmosphere of a character indicatortube for displaying side-by-side characters, the tube having a pluralityof anodes, one in each character position, and a plurality of groups ofcathodes each located in one of the characters positions, the cathodesin each group each being in the shape of a segment of a character to bedisplayed, including first circuit means including a plurality ofcathode conductors each making electrical connection to one of thecathodes in each character position, a plurality of cathode drivers,each connected to one of said cathode conductors, for energizingdifferent combinations of said cathodes in response to differentcombinations of electrical signals received by said cathode drivers,anode selection circuit means for sequentially energizing said anodes,in sychronism with the selective energization of said cathodes, fordisplaying selected characters in each of said character positions, biascircuit means for establishing a dynamic voltage bias on the auxiliaryelectrode, said circuit means including impedance means connectedelectrically to each of said anode selection circuits for developingacross said impedance means a series of bias voltage signals as theanodes are sequentially energized, one such signal being generatedduring the energization of each anode, and circuit means electricallyconnecting said impedance means to said auxiliary electrode to supplysuch series of bias voltage signals to said auxiliary electrode, andcircuit means connecting said cathode driver across at least a portionof said impedance means so as to modify the effective impedanceconnected to said auxiliary electrode as each cathode driver isenergized.
 9. Multiple-position display device and system for operatingthe device, said device comprising a gas-gilled envelope including aplurality of groups of cathode electrodes and an anode electrodeassociated with each said group, each such group of cathode electrodesand its anode electrode comprising a character position in said displaydevice, corresponding cathodes of the different groups beinginterconnected by a single common conductor, there thus being a singlecommon cathode conductor for each cathode electrode in each of saidgroups, and an auxiliary electrode in operative relation with all ofsaid groups of cathode electrodes and their anode electrodes andincluding a portion disposed between each anode and the adjacent groupsof cathodes to act as a shield therebetween, said system comprising aseparate anode driver circuit connected to each said anode electrode insaid display device, a sequencing circuit coupled to all of said anodedrivers for turning each one on separately and in turn whereby eachanode can be connected in circuit with a selected group of cathodeelectrodes, a separate cathode driver circuit connected to each of saidcommon cathode conductors, each such driver circuit thus being connectedto the same corresponding cathode in each of said groups of cathodes, asource of data signals coupled to said cathode driver circuits forenergizing a selected group of cathodes as each anode is connected incircuit, and a common impedance connected in circuit with all of saidanode drivers and with all of said cathode drivers and with saidauxiliary electrode whereby at each said character position in saiddisplay deivice when a character is displayed by a selected number ofcathode electrodes, a bias voltage is developed across said impedanceand is applied to said auxiliary electrode, said bias voltage beingrelated to the number of cathode electrodes energized and exhibitingcathode glow and conducting current at each character position. 10.Multiple-position display device and system for operating the deivce,said device comprising a gas-filled envelope including a plurality ofgroups of cathode electrodes and an anode electrode associated with eachsaid groUp, each such group of cathode electrodes and its anodeelectrode comprising a character position in said display device,corresponding cathodes of the different groups being interconnected by asingle common conductor, there thus being a single common cathodeconductor for each cathode electrode in each of said groups, and anauxiliary electrode in operative relation with all of said groups ofcathode electrodes and their anode electrodes and including a portiondisposed between each anode and the adjacent groups of cathodes andserving as a shield therebetween, said system comprising a separateanode driver circuit connected to each said anode electrode in saiddisplay device, a sequencing circuit coupled to all of said anodedrivers for turning each one on separately and in turn whereby eachanode can be connected in circuit with a selected group of cathodeelectrodes, a separate cathode driver circuit connected to each of saidcommon cathode conductors, each such driver circuit thus being connectedto the same corresponding cathode in each of said groups of cathodes, asource of data signals coupled to said cathode driver circuits forenergizing a selected group of cathodes as each cathode is connected incircuit; a first current flow path from each of said anode driversthrough separate resistive paths to all of said cathode drivers, asecond current flow path from each of said anode drivers through aresistive path to said auxiliary electrode, and a third current flowpath from each of said anode drivers to its anode and through saiddisplay device to its group of cathode electrodes.